It is the object of the invention to improve the tensioning behavior of such belt tensioner as well as to ensure reliable functioning of the belt tensioner even after quite long storage in the vehicle. It is another object of the invention to provide a simpler method of mounting a belt tensioner of this type.
For achieving the object in a belt tensioner of the type mentioned in the beginning it is provided that between the piston and the thrust means a spacer in the form of a separate member is provided to be dimensioned so that in the final position of the piston the thrust means is urged past the stop and especially out of the pressure reservoir by said spacer.
This spacer moving the thrust means past the stop ensures that, when the final position of the piston is reached, the thrust means cannot get caught at the projection or cannot be decelerated by the same. The thrust means is accelerated and, resp., driven until it has been moved completely past the projection and subsequently can move freely.
In order to safeguard that the thrust means is thrusted completely past the stop, the length of the spacer is preferably equal to or larger than the length of the stop in the longitudinal direction of the pressure reservoir. In addition, the spacer may be dimensioned such that it gets caught at the stop or is jammed at the same so that it cannot exit the pressure reservoir.
Preferably the length of the spacer is dimensioned so that in the final position of the piston the thrust means is completely forced out of the pressure reservoir. When, after activating the belt tensioner, force limitation takes place at the belt retractor, the gearwheel interacting with the thrust means and being coupled to the belt reel is rotated in a direction opposite to the tensioning case. If the thrust means still protruded partly into the pressure reservoir, it would be urged into the pressure reservoir again by the opposite rotation of the gearwheel. The resistance when thrusting the thrust means into the pressure reservoir would cause a change in the characteristic of the force limitation. When the thrust means is completely forced out of the pressure reservoir, however, free movement of the gearwheel, even with the coupled thrust means, is possible as the latter is equally adapted to move freely.
The spacer and the piston may enter in positive engagement so that a better hold and a better force transmission between the same are ensured. Moreover, the spacer is prevented in this way from being freely movable, especially after the tensioning case has been activated and the thrust means has left the pressure reservoir.
Coupling of the spacer and of the piston may be performed, for example, by a projection provided on the spacer and/or on the piston. Said spacer preferably engages in a recess on the piston side or on the spacer side, or vice versa.
Moreover, for achieving the object it is provided for a belt tensioner of the type mentioned in the beginning, especially for a belt tensioner according to the invention, that in a home position of the piston prior to activation of the belt tensioner the stop fixes, and especially clamps, the thrust means within the pressure reservoir. Hence the thrust means is safely fixed in the pressure reservoir by the projection so that it cannot move out of the pressure reservoir slowly by the vibrations occurring in the vehicle.
For example, the stop may be formed by an embossing of the pressure reservoir by which the cross-section of the pressure reservoir is narrowed so that the thrust means is jammed within the pressure reservoir. This type of manufacture of the projection enables the projection to be easily introduced into the pressure reservoir. Moreover, it is possible in this way to initially insert the thrust means into the pressure reservoir and to subsequently fix it by introducing the projection. In this way, the mounting of the belt tensioner, especially of the thrust means, in the pressure reservoir is substantially facilitated.
For achieving the object moreover a method of mounting a belt tensioner is provided comprising the following steps of:
a) inserting the thrust means into the pressure reservoir, and
b) subsequently introducing the stop into the pressure reservoir, with the thrust means being fixed by the stop in the pressure reservoir.
Consequently, the projection is not introduced before the thrust means has been inserted so that the thrust means can be inserted into the pressure reservoir without any resistance. In this way the mounting is substantially facilitated, but also the thrust means can be prevented from being damaged during mounting by a projection already provided in the pressure reservoir.
Preferably, the stop is manufactured by embossing.